Coated sheet materials having high solar reflective index and corrosion resistance, and methods of making same

ABSTRACT

Coated sheet materials having high solar reflective index and corrosion resistance, and methods of making such coated sheet materials, are disclosed. In certain embodiments, the sheet materials comprise metal such as galvanized steel roofing sheets, and the coating is deposited from a latex resin.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional PatentApplication Ser. No. 61/661,532 filed Jun. 19, 2012, which isincorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to coated sheet materials having highsolar reflective index and corrosion resistance, and methods of makingsuch coated sheet materials.

BACKGROUND OF THE INVENTION

Sheet materials used in architectural and other applications oftenrequire corrosion resistant properties. For example, steel and othertypes of metal roofing sheet materials must withstand exposure toenvironmental conditions for extended periods of time. Galvanized steelroofing sheets have conventionally been pre-treated withchromium-containing compositions to increase corrosion resistance. Suchpretreatments may be conducted on long strips of the steel, which arethen coiled into rolls for subsequent use.

Galvanized steel and other types of metal roofing materials may havehigh solar reflectance properties, but they tend to heat up when exposedto sunlight due to their low thermal emittance properties. As a resultof such solar heating, the underlying structures can require significantamounts of energy to cool, e.g., by air conditioning.

Several recent US and state government regulations require metal roofingto meet certain solar reflective index values to avoid overheating.Solar reflective index (SRI) is calculated based upon the combination ofsolar reflectance and thermal emittance, with an SRI value of 65, 70 orhigher being required to meet certain government regulations. Solarreflectance is measured as a percentage of solar radiation in thevisible, infrared and ultraviolet regions of the electromagneticspectrum that is reflected from a surface, with a value of 0 or 0%corresponding to zero reflectance and a value of 1 or 100% correspondingto total reflectance. Thermal emittance is measured as the ability of asurface to shed heat, with a value of 0 or 0% corresponding to zerothermal emittance and a value of 1 or 100% corresponding to totalthermal emittance. In order to reduce overheating, metal roofing withboth relatively high solar reflectance and thermal emittance is desired.

Conventional metal roofing fails to meet certain government energyregulations, and the use of conventional pretreatments decreases thesolar reflective index below that of the untreated metal.

SUMMARY OF THE INVENTION

An aspect of the invention provides a coated metal sheet comprising ametal substrate, and a cured coating covering at least a portion of themetal substrate, wherein: (a) the cured coating: (i) is deposited from acomposition comprising a latex resin, (ii) is substantially clear, (iii)is substantially free of reflective pigments, and (iv) has a dry filmthickness of at least 1 micron; and (b) the coated metal sheet has asolar reflective index of at least 65 and a corrosion resistance of atleast 500 h with no corrosion spots when subjected to an ASTMB117 saltspray test.

Another aspect of the invention provides a coated roof sheeting materialcomprising a sheet metal substrate, and a coating covering at least aportion of the sheet metal substrate, wherein the coating consistsessentially of a cured latex resin, and wherein the coated roof sheetingmaterial has a solar reflectance of at least 65 percent, a thermalemittance of at least 40 percent, and a corrosion resistance of at least500 h with no corrosion spots when subjected to an ASTMB117 salt spraytest.

A further aspect of the invention provides a method of coating a sheetmetal substrate comprising applying a coating composition comprising alatex resin that is substantially free of reflective pigments to thesheet metal substrate at a wet film thickness of at least 1 micron, andcuring the coating composition to produce a coated metal sheet having asolar reflective index of at least 65 and a corrosion resistance of atleast 500 h with no corrosion spots when subjected to an ASTMB117 saltspray test.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partially schematic side view of a coated roof sheetingmaterial in accordance with an embodiment of the present invention,illustrating solar reflectance and thermal emittance properties.

FIG. 2 is a partially schematic side view illustrating a method ofcoating and coiling metal sheets in rolling mill, including the use of aroll coater for applying a coating composition to the sheets inaccordance with an embodiment of the present invention.

FIG. 3 is a graph of total solar reflectance (TSR) vs. dry filmthickness (DFT) for coated metal sheets in accordance with embodimentsof the present invention.

FIG. 4 is a graph of thermal emittance (TE) vs. DFT for coated metalsheets in accordance with embodiments of the present invention.

FIG. 5 is a graph of solar reflective index (SRI) vs. DFT for coatedmetal sheets in accordance with embodiments of the present invention.

FIG. 6 is a graph of TSR vs. DFT for coated metal sheets in accordancewith embodiments of the present invention.

FIG. 7 is a graph of TE vs. DFT for coated metal sheets in accordancewith embodiments of the present invention.

FIG. 8 is a graph of SRI vs. DFT for coated metal sheets in accordancewith embodiments of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

FIG. 1 schematically illustrates a coated sheet material 10 inaccordance with an embodiment of the present invention including asubstrate sheet 12 and a coating layer 14. In certain embodiments, thecoated sheet 10 may be used in architectural applications, such as roofsheeting material for a building 16 or other structure. The coating 14has a dry film thickness T typically greater than 1 micron, for example,greater than 2 or 3 microns. In certain embodiments, the dry filmthickness T of the coating 14 may be from 3 to 10 or 20 microns. Thesubstrate sheet 12 may be of any desired thickness, such as from 0.5 to3 mm. For example, the thickness of galvanized steel roof sheetingmaterials may range from 0.5 to 2 mm in certain embodiments. Althoughthe sheet 12 shown in FIG. 1 is flat, any other shape may be provided,such as corrugated, ribbed, and the like.

As illustrated in FIG. 1, a portion of solar radiation incident on thecoated sheet 10 is reflected from its surface with a total solarreflectance TSR value. As used herein, the term “total solarreflectance” means a measure of the ability of a surface material toreflect sunlight—including the visible, infrared, and ultravioletwavelengths—on a scale of 0% to 100%. In certain embodiments, the totalsolar reflectance TSR of the coated sheet 10 is at least 60%, forexample, at least 62% or 65%.

As further illustrated in FIG. 1, the coated sheet 10 has thermalemittance TE properties. As used herein, the term “thermal emittance”refers to the ability of a material to release absorbed heat. A numberbetween 0 and 1, or 0% and 100%, is used to express emittance. Incertain embodiments, the thermal emittance TE of the coated sheet 10 isat least 0.3 (30%), for example, at least 0.4 (40%) or 0.5 (50%).

The total solar reflectance TSR and emittance TE properties, asschematically illustrated in FIG. 1, may be combined to yield a solarreflective index (“SRI”). As used herein, the term “solar reflectiveindex” is a value that incorporates both solar reflectance and emittancein a single value to represent a material's temperature in the sun. SRIquantifies how hot a surface would get relative to standard black andstandard white surfaces. It is calculated using equations based onpreviously measured values of solar reflectance and emittance as laidout in the American Society for Testing and Materials Standard E 1980.In accordance with ASTM Standard E 1980, values of TSR and TE are inputinto a standard equation to calculate the SRI value. In certainembodiments, the solar reflective index SRI is at least 65, for example,at least 70 or 75.

In accordance with embodiments of the invention, the coating compositioncomprises a latex resin. The latex resin may, or may not, beself-crosslinking. The latex resin typically comprises from 20 to 60weight percent of the coating composition, for example, from about 30 toabout 50 weight percent. In certain embodiments, suitable monomers usedfor preparing the latex resins may include vinyl aromatic monomers suchas styrene, cycloaliphatic monomers such as cyclohexyl methacrylate, andlong-chain aliphatic monomers such as 2-ethylhexyl acrylate, MMA and/or2-ethylhexyl methacrylate. Other types of monomers include cyclohexene,2-ethyl-1-hexene, cyclohexanol, alpha-methylstyrene, 2-ethylhexanol,2-ethylhexyl acetate, methyl-4-phenyl butyrate, methyl myristate and/ormethyl palmitate.

In certain embodiments, the monomers used in the latex resin comprise avinyl aromatic compound, such as a vinyl aromatic monomer, which, incertain embodiments, comprises a compound that has a calculated Tg ofleast 100° C. Specific examples of vinyl aromatic compounds are styrene(which has a calculated Tg of 100° C.), α-methylstyrene (which has acalculated Tg of 168° C.), vinyltoluene, p-methylstyrene,ethylvinylbenzene, vinylnaphthalene, vinylxylenes, α-methylstyrene dimer(meth)acrylate, penta fluoro styrene, and the like. In certainembodiments, styrene or another vinyl aromatic monomer may comprise themost predominant monomer of the resin on a weight percent basis.

In certain embodiments, the monomers of the latex resin includecycloaliphatic(meth)acrylate monomers, such as trimethylcyclohexylacrylate, t-butyl cyclohexyl acrylate, dicyclopentadiene(meth)acrylate,trimethylcyclohexyl methacrylate (calculated Tg of 98° C.), cyclohexylmethacrylate (calculated Tg of 83° C.), isobornyl methacrylate(calculated Tg of 110° C.), 2-ethylhexyl methacrylate,tetrahydrofurfuryl methacrylate, 3,3,5-trimethylcyclohexyl methacrylate(calculated Tg of 125° C.), and/or 4-t-butylcyclohexyl methacylate, andthe like.

In certain embodiments, the monomers of the latex resin include analkyl(meth)acrylate, which, in certain embodiments, comprises a compoundthat has a calculated Tg of least 100° C. Specific examples ofalkyl(meth)acrylates are C₁-C²⁴ alkyl(meth)acrylates, such asmethyl(meth)acrylate (which has a calculated Tg of 105° C.),propyl(meth)acrylate, butyl(meth)acrylate, isobutyl(meth)acrylate,hexyl(meth)acrylate, 2-ethylhexyl(meth)acrylate, octyl(meth)acrylate,decyl(meth)acrylate, dodecyl(meth)acrylate, pentadecyl(meth)acrylate,hexadecyl(meth)acrylate, octadecyl(meth)acrylate, andnonadecyl(meth)acrylate, and mixtures thereof. Other monomers include,for example, nitriles, such as acrylonitrile and/or methacrylonitrile.

Some non-limiting examples of latex resins that may be used in thecoating compositions of the present invention are commercially availablefrom Nuplex, Lubrizol, Rohm and Haas, Alberdingk Boley Company, Omnovaand DSM Neoresins, such as Joncryl 1982, Caroboset CR-781, Alberdingk AC2403, Alberdingk 2360, Neocryl XK-98 and the like.

The latex resin may have an average particle size of from 50 nm to 300nm, for example from 60 nm to 100 or 150 nm; a glass transitiontemperature (T_(G)) of from −20 to 100° C., typically from zero to 20 or50° C.; and an acid number of from 0 to 20, typically from 2 to 10.

The coating compositions of the present invention may be waterborne. Incertain embodiments, water may comprise from 20 to 80 weight percent ofthe coating compositions, for example, from 50 to 65 weight percent. Incertain embodiments, the coating compositions comprise less than 10weight percent organic solvents, for example, less than 7 or 4 weightpercent, based on the total weight of the composition. The resin solidscontent of the coating compositions may be relatively high, for example,greater than 35 or 40 weight percent, based on the total weight of thecomposition.

The coating compositions may have little or no volatile organic content(VOC). For example, the coating compositions may comprise less than 1.5weight percent VOCs, for example, less than 1 or 0.5 weight percentVOCs, based on the total weight of the composition. In certainembodiments, the coating compositions are substantially free of VOCs.

The coating compositions may further comprise at least one coalescingagent in an amount of up to 10 weight percent, for example, in an amountof from 2 to 3 weight percent, based on the total weight of the coatingcomposition. Examples of suitable coalescing agents include butylcarbitol commercially available from Dow Chemical Company, Dowanol DPM,Dowanol DPnB, Dowanol PPh, butyl cellosolve or Dowanol DPnP. Inaccordance with embodiments of the present invention, the coalescingagents form a thin film around the latex resin particles, which helpsthem coalesce. Improved coalescence of the latex resin particles resultsin very fine particle sizes and a uniform microstructure, which providesimproved corrosion protection in comparison with other types of coatingshaving larger resin particle sizes. For example, in accordance withcertain embodiments of the present invention, the average resin particlesize may be less than 150 nanometers, for example, less than 100 or 80nanometers.

In certain embodiments, wax may be added to the coating compositions inamounts up to 10 weight percent, for example, from 0.5 to 3 weightpercent, based on the total weight of the coating composition. Suitabletypes of wax include Ceraflour 913, Worleeadd 352, Aquamat 272, Aquamat270, Aquacer 539, and combinations thereof. For example, wax sold underthe designation Aquamat 272 by BYK Chemie may be used. The type andamount of wax may be controlled in order to improve scratch resistanceof the coated sheet materials. For example, when the coated sheets areformed into coils, the use of wax additives may reduce or preventscratching during the coiling an uncoiling processes, as well as duringsubsequent installation and use of the coated sheet materials. Incertain embodiments, the amount of wax added to the coating compositionis limited in order to avoid unwanted slippage when the coated sheetsare coiled, e.g., to prevent unwanted “telescoping” of the coils due tolow friction between the adjacent coil layers.

Various other additives may optionally be added to the coatingcompositions in accordance with certain embodiments of the invention.For example, suitable additives include thickeners, defoamers,surfactants, rust inhibitors, pH control agents, silica, and tints.

Suitable thickeners include Acrysol ASE-60, Aquatix 8421, DSX-1550, andLaponite RD. When used, such thickening agents may be present in amountsup to 7 weight percent, for example, from 0.5 to 4 weight percent, basedon the total weight of the coating composition.

Suitable defoamers include BYK-011, BYK-20, BYK-32, BYK 34 and DrewplusL-419 available from Ashland in amounts up to 2 weight percent, forexample, from 0.1 to 0.5 weight percent, based on the total weight ofthe coating composition.

Suitable surfactants include Zonyl FSP available from DuPont, Surfynol104E available from Air Products, BYK 346, and BYK348 in amounts up to 2weight percent, for example, from 0.1 to 0.5 weight percent, based onthe total weight of the coating composition.

Suitable rust inhibitors include Halox 550, Halox Flash X-150, 330,Halox SZP-391, ammonium benzoate, and sodium nitrite in typical amountsup to 1 weight percent, for example, from 0.4 to 0.6 weight percent,based on the total weight of the coating composition.

In certain embodiments, the coating compositions are substantially freeof certain metal salts such as metal phosphates, phosphocarbonates andphosphosilicates. For example, the compositions may be substantiallyfree of zinc phosphate, calcium phosphate, calcium phosphosilicateand/or calcium-enriched silica.

Suitable pH control agents include any water soluble amine such asdimethylethanol amine (DMEA) available from Avecia in typical amounts upto 1 weight percent, for example, from 0.01 to 0.2 weight percent, basedon the total weight of the coating composition.

In accordance with certain embodiments of the invention, the coatingsare substantially free of chrome. In such embodiments, chrome is notpurposely added to the coating compositions and is only present in tracelevels or as an impurity.

In certain embodiments, chromate-containing materials may be added tothe coating compositions. Such chromate-containing coating compositionsmay be particularly useful as primer coatings. For example, strontiumchromate may be added in amounts up to 12 weight percent, for example,from 0.2 to 1 weight percent, based on the total weight of the coatingcomposition. Such strontium chromate-containing additives may provideimproved corrosion resistance properties. When used as primer coatings,the coating compositions may further include colorants and tintstypically used in primers, such as titanium dioxide and the like.

In certain embodiments, silica may be added to the coating compositions,for example, in amounts from 0.1 to 2 or 3 weight percent or more. Someexamples of silica include Lo-Vel 275 silica from PPG Industries andAerosil 200 silica from Air Products.

In certain embodiments, the coating compositions and cured coatings aresubstantially free of reflective pigments. As used herein, the term“reflective pigment” means plate-like or sheet-like interferencepigments such as mica, silicates, silicon dioxide and aluminum oxide.Solarflair 9870 from Eckart is an example of a reflective pigment. Asused herein, the term “substantially free of reflective pigments” meansthat the coatings have zero or minimal amounts of reflective pigmentswhile achieving the desired level of solar reflectance and/or solarreflective index. For example, the cured coatings may have less than 2or 1 weight percent reflective pigment. Although the coatings may besubstantially free of reflective pigments, they still maintainsufficient solar reflectance properties and solar reflective indexvalues, e.g., SRIs of 65 or greater. The cost of reflective pigmentadditives may thus be avoided, while still providing a desired level ofsolar reflectance.

In certain embodiments, at least one colored pigment or tint may beadded to the coating compositions. Colored pigments and tints aredifferent from reflective interference pigments and include standardinorganic and organic pigments, such as those found in conventionalpaints and primers. For example, various colored pigments are listed inthe Dry Color Manufacturers Association (DCMA) classifications. Suchcolored pigments and tints typically comprise particles havingsubstantially equiaxed morphologies, e.g., aspect ratios of about 1:1,in comparison with plate-like and sheet-like reflective interferencepigments having relatively high aspect ratios. One suitable type ofcolored pigment includes TiO₂ in an amount up to 35 weight percent, forexample, from 1 to 25 weight percent, based on the total weight of thecoating composition. Aquext white tint commercially available from PPGIndustries and Corrosperse 176E chrome tint commercially available fromWayne Pigments are examples of suitable tints.

In certain embodiments, the coating is substantially free of coloredpigments and tints. For example, the coatings may be substantially clearand colorless.

In certain embodiments, conductive particles such as graphenic carbonparticles may be added to the coating compositions in amounts of to 5weight percent, for example, from 1 to 2 weight percent, based on thetotal weight of the coating composition. Such graphenic carbon particlesmay provide improved thermal emissivity properties. The graphenic carbonparticles may be obtained from commercial sources, or may be made inaccordance with the methods and apparatus described in U.S. applicationSer. Nos. 13/249,315 and 13/309,894, which are incorporated herein byreference. Exemplary commercially available graphenic carbon particlesare available from Angstron and XG Sciences.

As used herein, the term “graphenic carbon particles” means carbonparticles having structures comprising one or more layers ofone-atom-thick planar sheets of sp²-bonded carbon atoms that are denselypacked in a honeycomb crystal lattice. The average number of stackedlayers may be less than 100, for example, less than 50. In certainembodiments, the average number of stacked layers is 30 or less, such as20 or less, 10 or less, or, in some cases, 5 or less. The grapheniccarbon particles may be substantially flat, however, at least a portionof the planar sheets may be substantially curved, curled, creased orbuckled. The particles typically do not have a spheroidal or equiaxedmorphology.

In certain embodiments, the graphenic carbon particles present in thecompositions of the present invention have a thickness, measured in adirection perpendicular to the carbon atom layers, of no more than 10nanometers, no more than 5 nanometers, or, in certain embodiments, nomore than 4 or 3 or 2 or 1 nanometers, such as no more than 3.6nanometers. In certain embodiments, the graphenic carbon particles maybe from 1 atom layer up to 3, 6, 9, 12, 20 or 30 atom layers thick, ormore. In certain embodiments, the graphenic carbon particles present inthe compositions of the present invention have a width and length,measured in a direction parallel to the carbon atoms layers, of at least50 nanometers, such as more than 100 nanometers, in some cases more than100 nanometers up to 500 nanometers, or more than 100 nanometers up to200 nanometers. The graphenic carbon particles may be provided in theform of ultrathin flakes, platelets or sheets having relatively highaspect ratios (aspect ratio being defined as the ratio of the longestdimension of a particle to the shortest dimension of the particle) ofgreater than 3:1, such as greater than 10:1.

In certain embodiments, the graphenic carbon particles used in thecompositions of the present invention have relatively low oxygencontent. For example, the graphenic carbon particles used in certainembodiments of the compositions of the present invention may, even whenhaving a thickness of no more than 5 or no more than 2 nanometers, havean oxygen content of no more than 2 atomic weight percent, such as nomore than 1.5 or 1 atomic weight percent, or no more than 0.6 atomicweight, such as about 0.5 atomic weight percent. The oxygen content ofthe graphenic carbon particles can be determined using X-rayPhotoelectron Spectroscopy, such as is described in D. R. Dreyer et al.,Chem. Soc. Rev. 39, 228-240 (2010).

In certain embodiments, the graphenic carbon particles used in thecompositions of the present invention have a B.E.T. specific surfacearea of at least 50 square meters per gram, such as 70 to 1000 squaremeters per gram, or, in some cases, 200 to 1000 square meters per gramsor 200 to 400 square meters per gram. As used herein, the term “B.E.T.specific surface area” refers to a specific surface area determined bynitrogen adsorption according to the ASTMD 3663-78 standard based on theBrunauer-Emmett-Teller method described in the periodical “The Journalof the American Chemical Society”, 60, 309 (1938).

In certain embodiments, the graphenic carbon particles used in thecompositions of the present invention have a Raman spectroscopy 2D/Gpeak ratio of at least 1.1, for example, at least 1.2 or 1.3. As usedherein, the term “2D/G peak ratio” refers to the ratio of the intensityof the 2D peak at 2692 cm⁻¹ to the intensity of the G peak at 1,580cm⁻¹.

In certain embodiments, the graphenic carbon particles used in thecompositions of the present invention have a relatively low bulkdensity. For example, the graphenic carbon particles used in certainembodiments of the present invention are characterized by having a bulkdensity (tap density) of less than 0.2 g/cm³, such as no more than 0.1g/cm³. For the purposes of the present invention, the bulk density ofthe graphenic carbon particles is determined by placing 0.4 grams of thegraphenic carbon particles in a glass measuring cylinder having areadable scale. The cylinder is raised approximately one-inch and tapped100 times, by striking the base of the cylinder onto a hard surface, toallow the graphenic carbon particles to settle within the cylinder. Thevolume of the particles is then measured, and the bulk density iscalculated by dividing 0.4 grams by the measured volume, wherein thebulk density is expressed in terms of g/cm³.

In certain embodiments, the graphenic carbon particles used in thecompositions of the present invention have a compressed density and apercent densification that is less than the compressed density andpercent densification of graphite powder and certain types ofsubstantially flat graphenic carbon particles. Lower compressed densityand lower percent densification are each currently believed tocontribute to better dispersion and/or rheological properties thangraphenic carbon particles exhibiting higher compressed density andhigher percent densification. In certain embodiments, the compresseddensity of the graphenic carbon particles is 0.9 or less, such as lessthan 0.8, less than 0.7, such as from 0.6 to 0.7. In certainembodiments, the percent densification of the graphenic carbon particlesis less than 40%, such as less than 30%, such as from 25 to 30%.

For purposes of the present invention, the compressed density ofgraphenic carbon particles is calculated from a measured thickness of agiven mass of the particles after compression. Specifically, themeasured thickness is determined by subjecting 0.1 grams of thegraphenic carbon particles to cold press under 15,000 pound of force ina 1.3 centimeter die for 45 minutes, wherein the contact pressure is 500MPa. The compressed density of the graphenic carbon particles is thencalculated from this measured thickness according to the followingequation:

${{Compressed}\mspace{14mu} {Density}\mspace{14mu} \left( {g/{cm}^{3}} \right)} = \frac{0.1\mspace{14mu} {grams}}{\Pi*\left( {1.3\mspace{14mu} {{cm}/2}} \right)^{2}*\left( {{measued}\mspace{14mu} {thickness}\mspace{14mu} {in}\mspace{14mu} {cm}} \right)}$

The percent densification of the graphenic carbon particles is thendetermined as the ratio of the calculated compressed density of thegraphenic carbon particles, as determined above, to 2.2 g/cm³, which isthe density of graphite.

In certain embodiments, the graphenic carbon particles have a measuredbulk liquid conductivity of at least 100 microSiemens, such as at least120 microSiemens, such as at least 140 microSiemens immediately aftermixing and at later points in time, such as at 10 minutes, or 20minutes, or 30 minutes, or 40 minutes. For the purposes of the presentinvention, the bulk liquid conductivity of the graphenic carbonparticles is determined as follows. First, a sample comprising a 0.5%solution of graphenic carbon particles in butyl cellosolve is sonicatedfor 30 minutes with a bath sonicator. Immediately following sonication,the sample is placed in a standard calibrated electrolytic conductivitycell (K=1). A Fisher Scientific AB 30 conductivity meter is introducedto the sample to measure the conductivity of the sample. Theconductivity is plotted over the course of about 40 minutes.

In accordance with certain embodiments, percolation, defined as longrange interconnectivity, occurs between the conductive graphenic carbonparticles. Such percolation may reduce the resistivity of the coatingcompositions. The conductive graphenic particles may occupy a minimumvolume within the coating such that the particles form a continuous, ornearly continuous, network. In such a case, the aspect ratios of thegraphenic carbon particles may affect the minimum volume required forpercolation. Furthermore, the surface energy of the graphenic carbonparticles may be the same or similar to the surface energy of theelastomeric rubber. Otherwise, the particles may tend to flocculate ordemix as they are processed.

The graphenic carbon particles utilized in the compositions of thepresent invention can be made, for example, by thermal processes. Inaccordance with embodiments of the invention, the graphenic carbonparticles are produced from carbon-containing precursor materials thatare heated to high temperatures in a thermal zone. For example, thegraphenic carbon particles may be produced by the systems and methodsdisclosed in U.S. patent application Ser. Nos. 13/249,315 and13/309,894.

In certain embodiments, the graphenic carbon particles may be made byusing the apparatus and method described in U.S. patent application Ser.No. 13/249,315 at [0022] to [0048] in which (i) one or more hydrocarbonprecursor materials capable of forming a two-carbon fragment species(such as n-propanol, ethane, ethylene, acetylene, vinyl chloride,1,2-dichloroethane, allyl alcohol, propionaldehyde, and/or vinylbromide) is introduced into a thermal zone (such as a plasma); and (ii)the hydrocarbon is heated in the thermal zone to a temperature of atleast 1,000° C. to form the graphenic carbon particles. In otherembodiments, the graphenic carbon particles may be made by using theapparatus and method described in U.S. patent application Ser. No.13/309,894 at [0015] to [0042] in which (i) a methane precursor material(such as a material comprising at least 50 percent methane, or, in somecases, gaseous or liquid methane of at least 95 or 99 percent purity orhigher) is introduced into a thermal zone (such as a plasma); and (ii)the methane precursor is heated in the thermal zone to form thegraphenic carbon particles. Such methods can produce graphenic carbonparticles having at least some, in some cases all, of thecharacteristics described above.

During production of the graphenic carbon particles by the methodsdescribed above, a carbon-containing precursor is provided as a feedmaterial that may be contacted with an inert carrier gas. Thecarbon-containing precursor material may be heated in a thermal zone,for example, by a plasma system. In certain embodiments, the precursormaterial is heated to a temperature ranging from 1,000° C. to 20,000°C., such as 1,200° C. to 10,000° C. For example, the temperature of thethermal zone may range from 1,500 to 8,000° C., such as from 2,000 to5,000° C. Although the thermal zone may be generated by a plasma system,it is to be understood that any other suitable heating system may beused to create the thermal zone, such as various types of furnacesincluding electrically heated tube furnaces and the like.

The gaseous stream may be contacted with one or more quench streams thatare injected into the plasma chamber through at least one quench streaminjection port. The quench stream may cool the gaseous stream tofacilitate the formation or control the particle size or morphology ofthe graphenic carbon particles. In certain embodiments of the invention,after contacting the gaseous product stream with the quench streams, theultrafine particles may be passed through a converging member. After thegraphenic carbon particles exit the plasma system, they may becollected. Any suitable means may be used to separate the grapheniccarbon particles from the gas flow, such as, for example, a bag filter,cyclone separator or deposition on a substrate.

Without being bound by any theory, it is currently believed that theforegoing methods of manufacturing graphenic carbon particles areparticularly suitable for producing graphenic carbon particles havingrelatively low thickness and relatively high aspect ratio in combinationwith relatively low oxygen content, as described above. Moreover, suchmethods are currently believed to produce a substantial amount ofgraphenic carbon particles having a substantially curved, curled,creased or buckled morphology (referred to herein as a “3D” morphology),as opposed to producing predominantly particles having a substantiallytwo-dimensional (or flat) morphology. This characteristic is believed tobe reflected in the previously described compressed densitycharacteristics and is believed to be beneficial in the presentinvention because, it is currently believed, when a significant portionof the graphenic carbon particles have a 3D morphology, “edge to edge”and “edge-to-face” contact between graphenic carbon particles within thecomposition may be promoted. This is thought to be because particleshaving a 3D morphology are less likely to be aggregated in thecomposition (due to lower Van der Waals forces) than particles having atwo-dimensional morphology. Moreover, it is currently believed that evenin the case of “face to face” contact between the particles having a 3Dmorphology, since the particles may have more than one facial plane, theentire particle surface is not engaged in a single “face to face”interaction with another single particle, but instead can participate ininteractions with other particles, including other “face to face”interactions, in other planes. As a result, graphenic carbon particleshaving a 3D morphology are currently thought to provide the bestconductive pathway in the present compositions and are currently thoughtto be useful for obtaining electrical conductivity characteristicssought by the present invention, particularly when the graphenic carbonparticles are present in the composition in relatively low amounts.

FIG. 2 schematically illustrates a roll coating method for applyingcoating compositions onto sheet materials in accordance with anembodiment of the present invention. In the embodiment shown, thecoating operation may be conducted in a conventional rolling mill. Metalsheet material, such as galvanized steel or the like, is provided in along strip 5 that passes under oppositely-rotating coating rollers 20and 22, which are fed with a supply of a coating composition 24. Theuncoated strip 5 passes under the coating rollers 20 and 22, where alayer of the coating composition 24 is deposited on the upper surface ofthe sheet material. The coated sheet material 10 may be formed into acoil 26 for storage and transportation for use in various applications,such as galvanized steel roof sheeting.

During the roll coating process, the coating composition is typicallyapplied to the sheet material 5 with a wet film thickness of at least 1micron, typically at least 1 or 5 microns. In certain embodiments, thewet film thickness of the coating material is from 5 to 15 or 20microns. In certain embodiments, the deposition rate of the coatingcomposition may be at least 200 ft/min, typically at least 300 ft/min or350 ft/min.

After application, the coating compositions typically dry and curequickly with minimal VOC emissions. Curing times are typically in lessthan 1 minute, for example, less than 10 or 5 seconds. Typical curingtemperatures are below 300° F., for example, below 275° or 250° F. Incertain embodiments, curing times may be less than 3 or 2 seconds attemperatures of 225° F. or 200° F., or less.

The dry film thickness of the cured coating is typically at least 1micron up to 15 or 20 microns. For example, the dry film thickness maybe from 5 to 10 microns. In accordance with the present invention, suchrelatively thin coating layers have been found to significantly increasethe solar reflective index of metal roof sheeting materials.

The following examples illustrate various aspects of the presentinvention, but are not intended to limit the scope of the invention.

Examples

Coating compositions were prepared and tested as described in Tables 1-4below.

TABLE 1 Coating Composition Nos. 1-3 Sample Sample Sample Components No.1 No. 2 No. 3 Acrylic Latex Resin 198.10 199.18 165.41 Deionized Water15.23 17.84 85.30 Defoamer 0.48 0.48 0.51 Surfynol Surfactant 1.04 1.041.06 Surfactant 1.04 1.04 1.06 Coalescing Agent 10.01 10.01 10.15 ChromeTint 5.98 — 5.98 White Tint — — 154.63 Rust Inhibitor 2.41 2.43 2.46Thickener 3.55 3.55 5.36 Deionized Water 3.55 3.55 0.54 pH Control Agent0.53 0.53 0.54 Deionized Water 0.53 0.53 0.54 Wax 3.64 3.64 10.52 TotalWeight in Grams 246.09 243.82 444.06

TABLE 2 Coating Composition No. 4 Components Sample No. 4 Latex Resin201.14 UC Intermediate¹ 22.27 Deionized Water 3.70 Defoamer 0.13 RustInhibitor Pigment 8.05 Surfactant 0.24 Silica 1.08 Deionized Water 0.10Total Weight in Grams 236.62 ¹Acrylic Emulsion Joncryl 538 (98.88);Defoamer (0.74); Deionized Water (5.0); Silica (25.11); CorrosionPigment (49.78); Reflective Pigment (25.11); and Defoamer (0.26).

The components listed in Tables 1 and 2 above were added together in theorder described in each table under gentle stirring. The coatingcompositions were allowed to equilibrate overnight before panelpreparation. Viscosity and pH were checked the next day. The coatingcompositions were applied to galvanized steel substrates using a wiredrawdown bar. The coated panels were placed in a conveyor oven set at atemperature to obtain a peak metal temperature of 190° F. in two secondsdwell time (line speed). The coated panels were tested, with the resultsshown in Table 3 below.

TABLE 3 Test Results Sample Sample Sample Sample No. 1 No. 2 No. 3 No. 4% Weight 41.82 41.62 45.0 44.03 Solids Viscosity 10-15 10-15 12-20  9-25(Seconds) (measured using #4 Zahn Cup at room temperature) Dry Film0.15-0.20 0.15-0.20 0.4-0.5 0.15-0.25 Thickness (mils) (mils) (mils)(mils) 3.8-5.1 3.8-5.1 10.2-12.7 3.8-6.4 (microns) (microns) (microns)(microns) Pencil HB-F HB-F HB-F B Hardness T-Bend 1/3 np/nc 1/3 np/nc1/3 np/nc 1/3 np/nc Reverse Pass Pass Pass Pass Impact X-Hatch Pass PassPass Pass Adhesion Butler No Corrosion No Corrosion No CorrosionCorrosion - fail Immersion Salt Spray No Black No Black No BlackCorrosion - fail Spots Spots Spots Wet Stack No Pressure No Pressure NoPressure Pressure Mottling Mottling Mottling mottling, black spots TSR(%) 66.8 65 70.7 66.8 TE (%) 54 58 78 54 SRI 71 69 84 71

In accordance with the pencil hardness test, ASTM D3363, a pencil isheld firmly against the coating at a 45 degree angle and pushed awayfrom the operator in a 0.25 inch stroke. Sufficient pressure is exerteddownward and forward either to cut or scratch the film. The process isrepeated down the hardness scale until a pencil is found that will notcut through the film to the substrate. The scale of hardness is: 6B(very soft) up to a 6H (very hard).

In accordance with the Butler immersion test, ASTM D870, panels with cutedges are placed in a cup of covered tap water, and placed in a humiditycabinet 100 F/100% humidity, for 1000 hours. The panels are then removedfrom the water, and visually evaluated for any red or white rust, blackspots and or blisters on the faces and edges of the panels.

In accordance with the salt spray test, ASTM B117, panels are placedwith taped cut edges in a 95 F/5% NaCl solution cabinet for 1000 hours.The panels are then removed from the cabinet and visually evaluated forany red or white rust, black spots and blister defects on the faces ofthe panels.

In accordance with the wet stack test, ASTM D7376-10A, panels aresprayed with DI-water, stacked face to face, and clipped together in abundle to simulate a wound coil. The bundles are placed in a 100 F/100%humidity cabinet for 1000 hours. The bundles are then removed andvisually evaluated for dark stains or white stains (pressure mottling).

Galvanized steel panels coated with compositions similar to Sample Nos.1 and 2 described above were tested for TSR, TE and SRI properties atvarious dry film thicknesses (DFT). The results are shown in the plotsof FIGS. 3, 4 and 5.

Galvanized steel panels coated with compositions similar to Sample Nos.1 and 2 described above, but with additions of interference pigmentavailable from Eckart under the designation SolarFlair in an amount of 5weight percent based on the total weight of the coating composition,were tested for TSR, TE and SRI properties at various dry filmthicknesses (DFT). The results are shown in the plots of FIGS. 6, 7 and8.

Different types of graphenic carbon were added in an amount of 1 weightpercent to coating compositions similar to Sample No. 1 above. SampleNo. 5 included graphenic carbon particles produced in accordance withU.S. patent application Ser. No. 13/309,894. Sample No. 6 includedcommercially available graphenic carbon particles from Angstron soldunder the designation N-006-010-P. Sample No. 7 included commerciallyavailable graphenic carbon particles from XG Sciences sold under thedesignation X-GNP-M-25. Panels were prepared by drawdown on a galvanizedsteel substrate at a film thickness of 5 microns. The panels were thencured at peak metal temperature of 190° F. for 2 seconds using aconveyer oven. The panels were tested, with the results shown below inTable 4.

TABLE 4 Test Results Sample % Graphene Diameter Thickness Salt Spray -No. Graphene Type (microns) (nm) SRV TE SRI 1000 h 1 0% NA NA NA 66.30.55 70 Excellent 5 1% Graphenic 59.7 0.54 59 very few Carbon blistersParticles 6 1% Commercially <14 10-20 42.2 0.72 41 Excellent availableN-006-010-P graphenic carbon 7 1% Commercially  25 6 59.5 0.56 60 denseavailable blisters X-GNP-M-25 graphenic carbon

For purposes of this detailed description, it is to be understood thatthe invention may assume various alternative variations and stepsequences, except where expressly specified to the contrary. Moreover,other than in any operating examples, or where otherwise indicated, allnumbers expressing, for example, quantities of ingredients used in thespecification and claims are to be understood as being modified in allinstances by the term “about”. Accordingly, unless indicated to thecontrary, the numerical parameters set forth in the followingspecification and attached claims are approximations that may varydepending upon the desired properties to be obtained by the presentinvention. At the very least, and not as an attempt to limit theapplication of the doctrine of equivalents to the scope of the claims,each numerical parameter should at least be construed in light of thenumber of reported significant digits and by applying ordinary roundingtechniques.

Notwithstanding that the numerical ranges and parameters setting forththe broad scope of the invention are approximations, the numericalvalues set forth in the specific examples are reported as precisely aspossible. Any numerical value, however, inherently contains certainerrors necessarily resulting from the standard variation found in theirrespective testing measurements.

Also, it should be understood that any numerical range recited herein isintended to include all sub-ranges subsumed therein. For example, arange of “1 to 10” is intended to include all sub-ranges between (andincluding) the recited minimum value of 1 and the recited maximum valueof 10, that is, having a minimum value equal to or greater than 1 and amaximum value of equal to or less than 10.

In this application, the use of the singular includes the plural andplural encompasses singular, unless specifically stated otherwise. Inaddition, in this application, the use of “or” means “and/or” unlessspecifically stated otherwise, even though “and/or” may be explicitlyused in certain instances.

It will be readily appreciated by those skilled in the art thatmodifications may be made to the invention without departing from theconcepts disclosed in the foregoing description. Such modifications areto be considered as included within the following claims unless theclaims, by their language, expressly state otherwise. Accordingly, theparticular embodiments described in detail herein are illustrative onlyand are not limiting to the scope of the invention which is to be giventhe full breadth of the appended claims and any and all equivalentsthereof.

We claim:
 1. A coated metal sheet comprising: a metal substrate; and acured coating covering at least a portion of the metal substrate,wherein: (a) the cured coating: (i) is deposited from a compositioncomprising a latex resin, (ii) is substantially clear, (iii) issubstantially free of reflective pigments, and (iv) has a dry filmthickness of at least 1 micron; and (b) the coated metal sheet has asolar reflective index of at least 65 and a corrosion resistance of atleast 500 h with no corrosion spots when subjected to an ASTMB117 saltspray test.
 2. The metal sheet of claim 1, wherein the latex resin isself-crosslinking.
 3. The metal sheet of claim 1, wherein the latexresin is prepared from at least one vinyl aromatic monomer.
 4. The metalsheet of claim 1, wherein the latex resin has an average particle sizeof from 50 to 300 nm.
 5. The metal sheet of claim 1, wherein the curedcoating has a dry film thickness of at least 2 microns.
 6. The metalsheet of claim 1, wherein the cured coating has a dry film thickness offrom 3 to 20 microns.
 7. The metal sheet of claim 1, wherein the curedcoating further comprises a coalescing agent, wax, viscosity enhancingagent and/or a thickening agent.
 8. The metal sheet of claim 1, whereinthe cured coating further comprises from 0.5 to 3 weight percent wax. 9.The metal sheet of claim 1, wherein the cured coating is substantiallyfree of chrome.
 10. The metal sheet of claim 1, wherein the curedcoating is substantially free of metal phosphate.
 11. The metal sheet ofclaim 1, wherein the cured coating comprises at least one chromate. 12.The metal sheet of claim 1, wherein the cured coating further comprisesa colored pigment or a tint.
 13. The metal sheet of claim 1, wherein thecured coating further comprises up to 6 weight percent of a reflectivepigment.
 14. The metal sheet of claim 1, wherein the cured coatingfurther comprises graphenic carbon particles.
 15. The rubber formulationof claim 14, wherein the cured coating comprises up to 5 weight percentof the graphenic carbon particles.
 16. The metal sheet of claim 1,wherein the metal is in the form of a coil.
 17. The metal sheet of claim1, wherein the metal substrate comprises a metal roofing sheet.
 18. Themetal sheet of claim 1, wherein the metal substrate comprises galvanizedsteel.
 19. The metal sheet of claim 1, wherein the coated metal sheethas a solar reflectance of at least
 65. 20. The metal sheet of claim 1,wherein the metal sheet has a thermal emittance of at least 40 percent.21. A coated roof sheeting material comprising: a sheet metal substrate;and a coating covering at least a portion of the sheet metal substrate,wherein the coating consists essentially of a cured latex resin, andwherein the coated roof sheeting material has a solar reflectance of atleast 65 percent, a thermal emittance of at least 40 percent, and acorrosion resistance of at least 500 h with no corrosion spots whensubjected to an ASTMB117 salt spray test.
 22. The coated roof sheetingmaterial of claim 21, wherein the sheet metal substrate comprisesgalvanized steel.
 23. The coated roof sheeting material of claim 22,wherein the galvanized steel is in the form of a coil.
 24. The coatedroof sheeting material of claim 21, wherein the coating is depositedfrom a composition comprising a latex resin and has a dry film thicknessof at least 1 micron.
 25. A method of coating a sheet metal substratecomprising: applying a coating composition comprising a latex resin thatis substantially free of reflective pigments to the sheet metalsubstrate at a wet film thickness of at least 1 micron; and curing thecoating composition to produce a coated metal sheet having a solarreflective index of at least 65 and a corrosion resistance of at least500 h with no corrosion spots when subjected to an ASTMB117 salt spraytest.
 26. The method of claim 25, wherein the coating composition iswaterborne.
 27. The method of claim 25, wherein the coating compositionfurther comprises a coalescing agent, wax, viscosity enhancing agentand/or thickening agent.
 28. The method of claim 25, wherein the coatingcomposition has a viscosity of at least 10 seconds measured by a No. 4Zahn cup at room temperature.
 29. The method of claim 25, wherein thelatex resin has a glass transition temperature of less than 50° C. 30.The method of claim 25, wherein the coating composition comprises lessthan 5 weight percent volatile organic solvent.
 31. The method of claim25, wherein the coating composition has a VOC of less than 1.5.
 32. Themethod of claim 25, wherein the coating composition is hydrophobic. 33.The method of claim 25, wherein the coating composition is substantiallyfree of chrome and metal phosphate.
 34. The method of claim 25, whereinthe coating composition is applied by roll coating.
 35. The method ofclaim 34, wherein the coating composition is applied at a rate of atleast 200 ft/min.
 36. The method of claim 25, wherein the coating iscured at a temperature of less than 250° for a time of less than 10seconds.
 37. The method of claim 25, further comprising forming thecoated metal sheet into a coil.